Yes to add to the other answers here, lava tubes are easiest to spot from orbit. And caves due to erosion features and landslip features far harder to spot. But may well be there, on Mars especially.
This is indirect evidence for possible vast underground caverns in the past on Mars.
Vast Systems of Ancient Caverns on Mars May Have Captured Enormous Floodwaters
And here is a 2001 paper that classifies some of the possible types of cave we might find on Mars.
THE HYPOTHESIS OF CAVES ON MARS REVISITED
This is indirect evidence for possible vast underground caverns in the past on Mars.
Vast Systems of Ancient Caverns on Mars May Have Captured Enormous Floodwaters
And here is a 2001 paper that classifies some of the possible types of cave we might find on Mars.
THE HYPOTHESIS OF CAVES ON MARS REVISITED
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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